The use of radiation shielding structures in nuclear technology is, of course, widespread. Such structures are generally fabricated from metal or concrete, utilizing virgin materials, and are designed to provide a relatively high neutron cross section to minimize the transmission of radiation from a space enclosed by the structures to the environment or to so reduce the energy of that radiation which is transmitted as to render it harmless. Radiation shielding structures can include housings for radioactive chambers including the core of a nuclear reactor, containment vessels which may be provided outwardly of the core or highly radioactive portions of the installation to serve as a housing, pipes through which radioactive fluids can pass, and even containers which may be used for the temporary or permanent storage or disposal of radioactive wastes.
In nuclear installations of the aforedescribed type, moreover, radioactive wastes are generated in operation or are created by the removal of radioactive parts of the structure as part of maintenance or replacement procedures. The term "radioactive waste" as used herein, therefore, should be understood to include not only the radioactive materials produced by the operation of an installation apart from the fuel products which are generally recovered, but also the piping, wall structure, machinery and like elements which have in the past created a disposal problem when replacement was required.
Disposal of such materials has posed a very significant problem since disposal sites and techniques for the safe disposal of radioactive storages are limited and costly. Indeed, the magnitude of the wastes has been a major factor in the decreased introduction of nuclear power in many parts of the world.